Control circuit



Dec. 3, 1935. Q ENT 2,022,983

CONTROL CIRCUIT Filed June so, 1952 INVENTOR H. C. SILEN T ATT RNEY Patented Dec. 3, 1935 I UNITED STATES PATENT OFFICE Electrical Research Products, Inc.,

New York,

N. Y., a corporation of Delaware Application June 30, 1932, Serial No. 620,199 13 Claims. (Cl. 179-100.3)

This invention relates to control circuits and particularly to circuits for controlling the mean position of the photographic impression pro duced by a system for recording modulated currents on a photographic medium.

An object of the invention is a control circuit which, after being energized by a voltage having an amplitude exceeding a predetermined value, aifects the control device to a degree determined by the predetermined value; and does not restore the controlled device for a predetermined time after the voltage ceases.

Another object of the invention is a control circuit in which the operating and restoring times of the controlled device may be predetermined substantially independently of each other.

A feature of the invention is the use of an asymmetrically conductive circuit element associated with the controlled device to prevent the device from restoring for a time determined by the amplitude of the voltage when the control circuit has been energized by a voltage having an amplitude exceeding a predetermined value.

Another feature of the invention is the use of a storage device supplied with energy from modulated currents through a network which controls the operating time of the controlled device.

A further feature of the invention is the use of a storage device which discharges through a network which controls the restoring time of the controlled device substantially independently of the operating time.

In a typical embodiment of this invention, the control circuit is associated with a system for recording modulated currents on a photographic medium. It will, however, be apparent to those skilled in the art that certain features of this invention are not limited to the specific control circuit disclosed but are applicable to many other control circuits.

In known systems of recording modulated currents on a sensitive medium, the recording device causes a variation in the amount of radiant energy impressed in unit time on an area extending substantially the full width of the record and of small height lengthwise of the record. In the absence of modulated currents, a constant mean value of radiant energy is plied to the recording device, the radiant energy is varied above and below this mean value.

Recent experiments have shown that the noise currents produced during the reproduction of a positive copy of the record will be reduced in absolute magnitude if the mean value of the impressed on the recording area. When modulated currents are apradiant energy impressed on the medium in recording is at all times as small as possible.

In the present invention, the recording device is controlled so that the mean value or position of the radiantenergy impressed on the medium is caused to vary with the envelope of the amplitude variations of the modulated currents. A control circuit actuated by the modulated currents controls the recording device.

The recording device is mechanically adjusted c that the mean value or position of the radiant energy is in the center of the available range of the desired characteristic of the medium. A unidirectional current or voltage, which may be termed a static bias is applied to the recording 15 device to cause the recording device to reduce the exposure produced by the radiant energy impressed on the medium. A portion of the modulated currents are supplied to the control circuit and produce a current or voltage varying with the amplitude of the modulated currents. This current or voltage, which may be termed a dynamic bias is applied to the recording device in such direction as to oppose the effect of the static bias on the recording device.

The dynamic bias must obviously modify the static bias sufliciently to permit the recording device to be modulated by whatever amplitude of modulated currents may at the time be applied to the system. The control circuit should accordingly operate at least as rapidly as the variation in the envelope of the amplitudes of the modulated currents. The control circuit should not, however, be sensitive enough to follow the variations of an individual low frequency wave as a variation of this character will produce a distortion of the recorded wave form.

In accordance with the present invention the control circuit varies the mean value or position of the radiant energy impressed on the medium in accordance with the rate'of change of the initial portion of the envelope of the amplitudes of the modulated currents. The rate of restoration of the recording circuit to its initial conditions is adjustable substantially independently of the rate of operation of the control circuit. When the control circuit has been energized by modulated waves having an amplitude exceeding a predetermined value, a controllable time elapses before the recording circuit commences to restore to its initial condition.

In a typical embodiment of the invention, modulated currents, suitably amplified, are supplied through a rectifier to a device capable of storing electric energy, such as a shunt capacitor, 5

'late'd currents having an amplitude exceeding a a series inductance, etc. The voltage developed across the storage device is applied to a network containing the recording device and opposes the efiect of the static bias on the recording device. The time interval between the application of the modulated currents and the corresponding effect on the recording device, which may be termed the operating time, will be determined largely by the internal resistance of the rectifier added to the value of any resistance network which may be inserted in the circuit from the rectifier to the storage device.

The time interval after the modulated waves have ceased until the recording device is restored to its initial position may be termed the restoring time. When the control circuit has been energized by modulated currents having an amplitude less than a predetermined value, the restoring time is determined by the discharge of the storage device through a resistance network containing the recording device, and may be determined by the values of the network substantially independently of the operating time.

An asymmetrically conductive device is connected in series with the recording device, so that a modulated current of abnormal amplitude can not cause the dynamic bias to reverse the effect of the static bias on the recording device and thus cause a photographic overload. When the control circuit has been energized by modupredetermined value, due to the presence of this asymmetrically conductive device, an appreciable time will elapse after the modulated current ceases before the recording device will commence to restore. This time interval is determined by the value of the asymmetrical resistance and of the other elements in the resistance network into which the storage device discharges.

In a practical embodiment of the invention, operating times from a few milliseconds to over fifty milliseconds have been obtained. Normal restoring times of thirty to one hundred milliseconds have been obtained, and for modulatedcurrents of abnormal amplitude, the restoring time ,may increase to one or two-tenths of a second.

The drawing represents in schematic form a typical embodiment of the invention.

Light from a suitable source I is focused by a lens system 2 on aligned apertures 3 pierced in the pole faces of a permanent magnet 4. The light emerging from the apertures 3 is focusedby a lens system 5 on a film 6, moved at constant speed in the known manner by the drive sprockets 1, 8. An opaque plate 9 pierced by an aperture It limitsthe exposed area of the film 6. A pair of conductive ribbons II, I2, which may be parts of a single ribbon, limit the height of the recording beam lengthwise of the film. When an electric current flows in the ribbons II, I2, the reaction of the magnetic field due to this electric current. with the steady field produced by the magnet 4 will displace the ribbons II, I2 and increase or decrease the height of the recording beam impressed on the film.

For convenience of description, a recording device similar to the well known light valve dis-' closed in United States Patent 1,638,555 issued August 9, 1927 to E. C. Wente has been disclosed. The invention is not to be considered as limited to any specific type of recording device and obviously may be applied to other known types of recording devices such as vibrating mirrors, vi-

brating shutters, flashing lamps and many others.

Acoustic waves are detected by a conventional sound detector such as the microphone I3, and amplified in suitable amplifiers I4 and I5. A portion of the sound modulated currents are impressed on the primary winding of a transformer I6. The output of the transformer I6 is transmitted through a capacitor l1 to the ribbons II, I2 and cause the ribbons II, I2 to vibrate, thus varying the height of the recording beam in accordance with the instantaneous variations in the sound modulated currents.

A constant current fiows from battery I8 through wire I9, ribbons II and I2, wire 20, asymmetrically conductive device 2 I, variable resistor 22 and inductor 23 to battery I8. The value of this current may be adjusted by the resistor '22 so that, in the absence of modulated currents, the spacing of the ribbons II and I2 is reduced to any desired degree. It will be found that the noise produced during the reproduction of a positive print of the film sound record is reduced proportionately to the reduction in the This constant static in the storage device 25, which for convenience 80 is shown as a shunt capacitor. The energy stored in the capacitor 25 will depend on the voltage of the battery I8 and the resistance of the series elements in the above circuit. The variable re sistor 26 will largely control the time required for u the capacitor 25 to attain full charge. The value of the charge attained will also be affected by the current flowing in the branch circuit formed by the shunt resistor 28; by the current flowing in the branch circuit formed by the shunt re- 4 sistor 29 and series resistor 30.; and the branch circuit formed by the asymmetrically conductive elements 3|, 32, 33, 34 and the series resistor 35. The series resistor 35 may generally be replaced by the internal resistance of the network of asym- 45 metrically conductive elements 3|, 32, 33 and 34. Similarly, in many cases the resistors 29 and 3|] may be eliminated.

Modulated currents from the amplifier I5 may be further amplified in the amplifier 36 and sup- 50 i fiowing into the capacitor 25 will tend to reverse 60 the charge in the capacitor 25 due to battery I8. When the charge received by the capacitor 25 has reversed the previous charge, current will flow in resistor 28, and will also tend to fiow in the circuit formed by resistor 26, inductor 21, 65

resistor 22, inductor 23, battery l8 and wire 24. This increasing current flowing in resistor 22 will increase the voltage drop in the resistor 22, thus reducing the voltage supplied by the battery I8 to the circuit formed by wire I9, ribbons II and 70 I2, wire 20 and element 2 I. The current'fiowing in the ribbons II and I2 will decrease and the mean spacing of the ribbons will increase. The time required for the capacitor 25 to attain full reversal of its charge from battery I8 is largely dependent on the values of the resistors 35 and 30. For rapid operation, the series resistances 35 and 30 should be small and the shunt resistance 29 should be infinite. The charging time will, under these circumstances, be largely controlled by the shunt resistance 28, and, to a lesser degree, by the series resistances 26 and 22. The current from the capacitor 25 flowing in the resistance 22 may conveniently be termed a dynamic biasing current.

Assume that the rectified potential applied to the capacitor 25 is large enough and has existed for suflicient time that the potential drop in the resistance 22 equals the voltage of the battery la. The static biasing current in the ribbons H and i2 will then be zero, and the ribbons H and I2 will have a maximum spacing determined by their mechanical adjustment. The recording device will be capable of recording modulated currents of maximum amplitude. A further increase in the rectified potential will have no effect on the spacing of the ribbons H and I2, as the asymmetrically conductive element 2| prevents the dynamic biasing current from causing the static biasing current to be reversed.

Having charged the capacitor 25 to a potential difierence large enough to more than overcome the effect of the battery I8 on the ribbons I l and i2, let it be assumed that the voltage applied by the transformer 37 is decreased to zero. The

capacitor 25 can not discharge through the network of asymmetrical elements 3|, 32, 33 and '34. A portion of the discharge may pass through the resistor 29, but as previously discussed, resistor 29 will normally be of high or infinite resistance. The discharge will then pass largely through the two branch circuits, one formed by the resistor 28 and the other formed by the resistor-26, inductor 21, resistor 22, inductor 23 and battery is in series. The time of discharge will be largely controlled by the resistances 28 and 26. During this part of the discharge, the ribbons H and I2 retain their maximum spacing and are not affected by the discharge of the capacitor 25. This phase of the discharge will continue until the voltage lost in the resistance 22 becomes just equal to the voltage of the battery l8.

As the discharge of the capacitor 25 continues, the voltage lost in the resistance 22 becomes less than the voltage of the battery IS. The surplus of voltage from the battery I 8 is then effective to force a current through the ribbons H and I2 and thus cause the ribbons l l and I2 to reduce the height of the recording beam. The discharge of the capacitor 25 will continue until the capacitor 25 is completely discharged. The battery it will then charge the capacitor 25 again as previously described.

The charge received by the capacitor 25 is dependent on the amplitude of the modulated currents from the transformer 31. Thus, for modulated currents of small amplitude, the ribbons I I and i2 are close together and the height of recording beam is small. As the modulated c rients increase in amplitude, the spacing of i; 'ibb' nil and I2 increases. When the am- ,dulated currents reaches a cercing of the ribbons II and I2 a- 'e} and dd 5 rents will have noefieb on t ribbons. The time requir w be opened to their maximum sp very short.

I of the amplitudes of the When the capacitor 25 has been charged by modulated currents exceeding a certain maximum amplitude, and the amplitude of the modulated currents decreases, the capacitor 25 will commence to discharge. of the discharge, the spacing of the ribbons Ii and I2 remains unchanged at the maximum value. After the discharge has progressed to a point where the remaining potential difference of the capacitor 25 is below a certain value, the spacing of the ribbons H and I2 commences to decrease, and if the discharge continues, the spacing may decrease to a minimum. The time taken for the discharge to fall from its maximum value to the value at which the spacing 15 commences to decrease may be regulated. The time taken for the spacing to decrease from maximum to minimum may also be independently regulated. These time intervals may be so regulated that the spacing of the ribbons will in- 0 crease with the first half wave of the modulated currents, but will decrease-with the envelope modulated currents and wave.

not with an individual What is claimed is:

1. In combination, a device for recording modulated currents on a photosensitive material, means for rendering said device substantially inoperative in the absence of modulated currents, biasing means energized by said currents for rendering said device operative, means associated with said biasing means for controlling the time required to render said device operative, other means associated with said biasing means for controlling the time to restore said device to the inoperative condition after being energized by currents of a range of normal amplitudes, and means associated with said device for independently controlling the time to restore said device to the inoperative condition after being energized by currents of abnormal amplitude.

2. In a system for recording modulated currents on a photosensitive material, in combination, a device for recording said currents mechanically adjusted to locate the recording range in the center of a desired characteristic of said material, a static biasing voltage applied to said device to displace said recording range to the part of said characteristic at which the exposure of said material is a minimum control means energized by said currents to produce a dynamic biasing voltage opposing said static biasing voltage, means associatedwith said control means for controlling the rate of increase of said dynamic biasing voltage, and other means associated with 55 said control means for independently controlling the rate of decay of said dynamic biasing voltage.

3. In a system for recording modulated currents on a photosensitive material, in combination, a device for recording said currents mechanically adjusted to locate the recording range in the center of a desired characteristic of said material, means for applying a static biasing voltage to said device to displace said recording range to the part of said characteristic in which the exposure of said material is a minimum conbiasing voltage opposing said static biasing voltage, means associated with said control means for controlling crate of increase of said dynamic biasing volt- "their means associated with said control for ently controlling the rate of said yn abiasing voltage after said During the first part 5 ling the rate of increase control means have been energized by currents of a range of normal amplitudes, and means associated with said device for independently controlling the rate of decay of said dynamic biasing voltage after said control means have been energized by currents of abnormal amplitude.

4. In combination, a device actuated by electric currents, means for supplying a biasing voltage to render said device substantially inoperative, a control circuit energizedby modulated currents for supplying a voltage opposing the effect of said biasing voltage on said device, an input network in said control circuit for controlof said opposing voltage, a second network in said control circuit for controlling substantially independently of said input network, the rate of decay of said opposing voltage and an asymmetrically conductive element associated with said device for limiting the effect of said opposing voltage on said device.

5. In combination, a device actuated by electric currents, means comprising a source of biasing voltage and an adjustable resistance for ren-.

dering said device substantially inoperative, a source of unidirectional voltage opposing the effect of said biasing Voltage, meansfor storing electrical energy, an input network associated with said storage means for controlling the rate of increase of energy from said source of unidirectional voltage to said storage means and said device, an output network associated with said storage means for controlling the rate of release of energy from said storage means substantially independently of said input network, and an asymmetrically conductive element associated with said device for preventing the release of energy from said storage means from afiecting said device until the energy stored in Y said means has fallen below a predetermined value. V

6. A sound-on-film recording apparatus ineluding in combination a film advancing means,

means for directing a light beam to the film, a

microphone, an amplifier the input of which is connected to the microphone, aipower amplifier the input of which is connected to the output of the first amplifier, a second power amplifier connected to the output of the first amplifier, a rectifying net-work connected to the output of the second power amplifier and between the two power amplifiers, a recording lamp, 2. source of electrical energy connected to the output of the first power amplifier and also to the output of the net-work, and supplementing current source means maintained charged by means of the network whereby the output energy of the second power amplifier is at all times stored with current of unchanging polarity but in varying amounts at varying potentials.

11. A sound-'on-film recording apparatus as claimed in claim 6, wherein a supplementing current source means is a reservoir condenser and the rectifying net-work is a Wheatstone ridge.

12. A .sound-on-film recording apparatus as claimed in claim 6, wherein the second power amplifier is an output transformer and wherein th rectifying net work is a Wheatstone bridge.

13. A sound-on-film recording apparatus as claimed in claim 6, wherein the second power amplifier is an output transformer, the supplementing current source means is a reservoir condenser and the rectifying net-work is a Wheatstone bridge.

HAROLD C. SILENT. 6 

